Field of the Disclosure
This application relates generally to air core magnetic components. More particularly the present disclosure relates to high frequency cores made of a toroidal magnetic material that can be energized by passing electric current.
Description of the Related Art
A magnetic core is an important component of electrical, electromechanical and magnetic devices. The magnetic core confines and guides magnetic fields in a circuit. For example, a typical inductor consists of a coil that creates flux, a magnetic core that directs flux, and an air gap, that stores magnetic energy. The air gap is made of two flat faces of iron within the magnetic core. Several factors define the performance characteristics of a magnetic core including the geometry, permeability and hysteresis properties, amount of air gap, operating frequency, magnetic material, etc. Magnetic cores are available in many shapes each having different characteristic behavior. Typically, it is desired to select a magnetic core having highest efficiency, and low flux leakage.
Toroid shape magnetic cores are often found very effective for many wide band frequency application, power transformers, and inductors. The toroidal core is formed either by winding a thin strip of magnetic material continuously, like a tape, or by using powder iron that is pressed and compacted into toroidal shape. An ideal coil is distributed evenly all around the circumference of the toroid. The symmetry of this geometry creates a magnetic field of circular loops inside the core, and the lack of sharp bends will constrain virtually the entire magnetic field to the core.
SiC or GaN wide-band gap (WBG) semiconductors permit power electronics to have an operation frequency at least ten times higher than conventional Si device circuits, up to several MHz. Further, due to the AC characteristics of WBG semiconductors, fewer passive components are required. However, core materials for transformers have frequency limits.
Core losses are an important limitation in most high frequency applications for transformer. Common core losses occur due to a changing magnetic field such as hysteresis loss due to expansion and contraction of magnetic domain from changing magnetic field, eddy current losses due to induced circulating loops of current that generates heat and adds to the resistivity of the core, and skin effect due to increased current concentration at the surface of the conductor thus reducing its effective surface area in turn increasing the resistivity. Further, electromagnetic interference and electromagnetic compatibility are other issues related to high frequency devices.
A toroid shaped magnetic core offers lower core losses compared to other shapes. A wire wound toroid is widely used in several applications. However, the wire winding process can be expensive and results in a sub-optimal toroid configuration. More advanced toroidal core designs offering high quality factor, commonly referred to as Q-factor, which are needed with the increased demand of high frequency operation.